Referring to FIGS. 1A and 1B, it shows the normal flow of aquarium water through a conventional filter. As illustrated, the filter housing 10 comprises an intake chamber 13 and a filtering chamber 12 which are separated by a partition wall 11. A pump 14 is provided under the intake chamber 13. An impeller 15 is disposed in the intake chamber 13 and is rotatably coupled to the pump 14. A U-shaped intake tube 16 has one end positioned in an aquarium tank (not shown) and the other end proximate the impeller 15. Upon energizing the pump 14 and thus the impeller 15, water from the aquarium tank is sucked into the intake tube 16. Water then flows up through the intake tube 16 and is drawn into the intake chamber 13. The water filled in the intake chamber 13 will overflow the partition wall 11 into the filtering chamber 12 if it has a sufficient height. The filtration material provided in the filtering chamber 12 is used to filter the water. The filtered water then passes back into the aquarium tank.
Referring to FIG. 1C, it is assumed that power outage has occurred or the impeller 15 failed to operate normally due to a piece of debris getting stuck therein. When such stoppage occurs, water in the intake chamber 13 begins to reversely flow out of the intake chamber 13 due to a siphoning action since the filter is provided at a level higher than the external aquarium tank. At the same time, water in the filtering chamber 12 flows backward over the partition wall 11 for filling the intake chamber 13 prior to flowing back to the aquarium tank through the intake tube 16.
Referring to FIG. 1D, water in the intake chamber 13 is completely drained after water has gradually flowed back into the aquarium tank through the intake tube 16 and the water level of the filtering chamber 12 is no more higher than that of the intake chamber 13. At this time, the siphoning action stops. If the power to the pump 14 resumes, the filter will not begin but will remain in the stage shown in FIG. 1D. In order for the filter to begin, it must be primed whereby sufficient water is placed in the intake chamber 13 to cover the impeller 15 so that the impeller 15 will be able to spread water out and cause a reduced pressure thereby sucking in additional water. In the absence of such priming water, the filter will not restart and will remain in the state shown in FIG. 1D. However, since the electricity will begin flowing to the pump 14, the pump 14 will heat up. Since there is no circulating water in the pump 14, the pump 14 will continue to generate heat. This heat may cause damage to the intake chamber 13. Moreover, the failure of the filter to provide adequate filtration to the aquarium tank may cause damage and harm to the contents of the aquarium itself.
U.S. Pat. No. 4,761,227 discloses a self priming aquarium filter for overcoming the above drawback as illustrated in FIGS. 2A and 2B. A narrow passageway 27 is provided in the partition wall 21. The cross-sectional area of the passageway 27 is less than that of the intake tube 26. Accordingly, after the majority of water has flowed over the partition wall 21 (see FIG. 2B), and when water level of the filtering chamber 22 has reached the upper end of the partition wall 21, a small trickle flow will still flow through the passageway 27 from the filtering chamber 22 back into the intake chamber 23. But the siphoning action of the intake tube 26 with respect to the intake chamber 23 will operate faster than the trickle flow. Hence, the siphoning flow will cause the water to drain out of the intake chamber 23 faster than the trickle flow flows into the intake chamber 23. As an end, the water will deplete from the intake chamber 23 beneath the level of the impeller 25. Thereafter, the siphon breaks and no more water will flow outwardly from the intake chamber 23. When this occurs, the continuous trickle flow passing through the passageway 27 will now begin accumulating in the intake chamber 23. As a result, the intake chamber 23 is filled with sufficient priming water. Upon resumption of power, the filter and thus the impeller 25 will automatically start a normal operation without adding priming water manually. The patent aids in permitting the siphoning action to break prior to providing a sufficient trickle flow to reprime the filter.
Taiwanese Patent Application No. 93,112,070, entitled “Aquarium Filter Having Check Valve”, as invented by the present inventor is shown in FIGS. 3A and 3B. A check valve 32 is provided in a vertical portion of the intake tube 30. In operation (i.e., the pump 33 is energized) as shown in FIG. 3A, water flows from the aquarium tank to the intake chamber 31 via the intake tube 30 and the check valve 32. In an inoperative state of the filter (i.e., the pump 33 is deenergized) as shown in FIG. 3B, the inlet 34 of the check valve 32 is completely blocked due to its spring mechanism. As such, a small trickle flow due to the siphoning action of the intake tube 30 will not flow through the check valve 32. As a result, sufficient water is placed in the intake chamber 31 for ensuring a self-priming of the filter when power resumes. While it is advantageous in the self-priming arrangement, the provision of the check valve 32 can increase the difficulty of assembly, the complexity of parts, and cost. Thus, the need for improvement still exists.